# Reflecting telescope

Telescope that uses a single or a combination of curved mirrors that reflect light and form an image.

- Reflecting telescope

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## Chromatic aberration

Failure of a lens to focus all colors to the same point.

Isaac Newton's theories about white light being composed of a spectrum of colors led him to the conclusion that uneven refraction of light caused chromatic aberration (leading him to build the first reflecting telescope, his Newtonian telescope, in 1668.

## Parabolic reflector

Reflective surface used to collect or project energy such as light, sound, or radio waves.

In optics, parabolic mirrors are used to gather light in reflecting telescopes and solar furnaces, and project a beam of light in flashlights, searchlights, stage spotlights, and car headlights.

## Objective (optics)

Optical element that gathers light from the object being observed and focuses the light rays to produce a real image.

In a telescope the objective is the lens at the front end of a refracting telescope (such as binoculars or telescopic sights) or the image-forming primary mirror of a reflecting or catadioptric telescope.

## James Gregory (mathematician)

Scottish mathematician and astronomer.

He described an early practical design for the reflecting telescope – the Gregorian telescope – and made advances in trigonometry, discovering infinite series representations for several trigonometric functions.

## Curved mirror

Mirror with a curved reflecting surface.

The most common non-spherical type are parabolic reflectors, found in optical devices such as reflecting telescopes that need to image distant objects, since spherical mirror systems, like spherical lenses, suffer from spherical aberration.

## Telescope

Optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects, or various devices used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation.

The reflecting telescope, which uses mirrors to collect and focus light, was invented within a few decades of the first refracting telescope.

## Newtonian telescope

The Newtonian telescope, also called the Newtonian reflector or just the Newtonian, is a type of reflecting telescope invented by the English scientist Sir Isaac Newton (1642–1727), using a concave primary mirror and a flat diagonal secondary mirror.

## Hubble Space Telescope

Space telescope that was launched into low Earth orbit in 1990 and remains in operation.

In 1968, NASA developed firm plans for a space-based reflecting telescope with a mirror 3 m in diameter, known provisionally as the Large Orbiting Telescope or Large Space Telescope (LST), with a launch slated for 1979.

## Primary mirror

A primary mirror (or primary) is the principal light-gathering surface (the objective) of a reflecting telescope.

## Refracting telescope

Type of optical telescope that uses a lens as its objective to form an image (also referred to a dioptric telescope).

Although large refracting telescopes were very popular in the second half of the 19th century, for most research purposes, the refracting telescope has been superseded by the reflecting telescope, which allows larger apertures.

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